[llvm] [AArch64][MachineCombiner] Reassociate long chains of accumulation instructions into a tree to increase ILP (PR #126060)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lldb-aarch64-windows` running on `linaro-armv8-windows-msvc-05` while building `llvm` at step 4 "build".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/141/builds/7268

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 4 (build) failure: build (failure)
...
256.841 [4752/10/1909] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\ValueTypes.cpp.obj
257.217 [4751/10/1910] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\SwiftErrorValueTracking.cpp.obj
257.372 [4750/10/1911] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\SplitKit.cpp.obj
257.453 [4749/10/1912] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\StackSlotColoring.cpp.obj
257.722 [4748/10/1913] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\WasmEHPrepare.cpp.obj
258.154 [4747/10/1914] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\WinEHPrepare.cpp.obj
261.189 [4746/10/1915] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\TailDuplicator.cpp.obj
261.538 [4745/10/1916] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LiveDebugValues\LiveDebugValues.cpp.obj
261.894 [4744/10/1917] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\TargetSchedule.cpp.obj
264.846 [4743/10/1918] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\TargetInstrInfo.cpp.obj
FAILED: lib/CodeGen/CMakeFiles/LLVMCodeGen.dir/TargetInstrInfo.cpp.obj 
ccache C:\Users\tcwg\scoop\apps\llvm\current\bin\clang-cl.exe  /nologo -TP -DGTEST_HAS_RTTI=0 -DUNICODE -D_CRT_NONSTDC_NO_DEPRECATE -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_SECURE_NO_DEPRECATE -D_CRT_SECURE_NO_WARNINGS -D_HAS_EXCEPTIONS=0 -D_SCL_SECURE_NO_DEPRECATE -D_SCL_SECURE_NO_WARNINGS -D_UNICODE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\lib\CodeGen -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\CodeGen -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\build\include -IC:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\include /DWIN32 /D_WINDOWS   /Zc:inline /Zc:__cplusplus /Oi /Brepro /bigobj /permissive- -Werror=unguarded-availability-new /W4  -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wmissing-field-initializers -Wimplicit-fallthrough -Wcovered-switch-default -Wno-noexcept-type -Wnon-virtual-dtor -Wdelete-non-virtual-dtor -Wsuggest-override -Wstring-conversion -Wmisleading-indentation -Wctad-maybe-unsupported /Gw /O2 /Ob2 /DNDEBUG -std:c++17 -MD  /EHs-c- /GR- /showIncludes /Folib\CodeGen\CMakeFiles\LLVMCodeGen.dir\TargetInstrInfo.cpp.obj /Fdlib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LLVMCodeGen.pdb -c -- C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\CodeGen\TargetInstrInfo.cpp
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\CodeGen\TargetInstrInfo.cpp(1514,29): error: non-const lvalue reference to type 'DenseMap<unsigned int, [...]>' cannot bind to a value of unrelated type 'DenseMap<Register, [...]>'
 1514 |                             InstIdxForVirtReg, Root.getOperand(0).getReg());
      |                             ^~~~~~~~~~~~~~~~~
C:\Users\tcwg\llvm-worker\lldb-aarch64-windows\llvm-project\llvm\lib\CodeGen\TargetInstrInfo.cpp(1021,35): note: passing argument to parameter 'InstrIdxForVirtReg' here
 1021 |     DenseMap<unsigned, unsigned> &InstrIdxForVirtReg,
      |                                   ^
1 error generated.
265.071 [4743/9/1919] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\TargetRegisterInfo.cpp.obj
268.058 [4743/8/1920] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\UnreachableBlockElim.cpp.obj
270.672 [4743/7/1921] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\VirtRegMap.cpp.obj
270.730 [4743/6/1922] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\XRayInstrumentation.cpp.obj
273.305 [4743/5/1923] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\TwoAddressInstructionPass.cpp.obj
273.358 [4743/4/1924] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\VLIWMachineScheduler.cpp.obj
275.926 [4743/3/1925] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\WindowScheduler.cpp.obj
281.777 [4743/2/1926] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LiveDebugValues\VarLocBasedImpl.cpp.obj
288.931 [4743/1/1927] Building CXX object lib\CodeGen\CMakeFiles\LLVMCodeGen.dir\LiveDebugValues\InstrRefBasedImpl.cpp.obj
ninja: build stopped: subcommand failed.

```

</details>

https://github.com/llvm/llvm-project/pull/126060